Temperature monitored cable system with telemetry read-out

ABSTRACT

In order to accurately and instantaneously measure the average temperatures of a plurality of intervals of a length of current carrying conductor such as a high-tension cable, a plurality of pilot wires each having a conductivity which varies according to its temperature is provided in thermal communication with corresponding intervals of the conductor along their common extents, so that the conductor and pilot wire are at essentially the same temperatures but are electrically insulated from one another. A circuit is provided for measuring the conductivity and thereby the temperature of each pilot wire, and a radio telemetry transmitter transmits this information to a receiver on the ground, from which it may be re-transmitted to any desired remote location.

United States Patent 1 Engelhardt et al.

[451 July 24, 1973 TEMPERATURE MONITORED CABLE SYSTEM WITH TELEMETRYREAD-OUT inventors: John Sherman Engelhardt,

Hartsdale', Lawrence Charles Ebel, Hastings-on-Hudson, both of N.Y.

The Anaconda Company, New York, N.Y.

Filed: June 17, 1971 Appl. No.: 154,146

Related US. Application Data Division of Ser. No. 839,571, July 7, l969,Pat. No 3,633,l9l, which is a continuation-in-part of Ser. No. 580,762,Sept. 20, 1966, Pat. No. 3,49i,597.

Assignee:

References Cited UNITED STATES PATENTS l0/l967 Bielstein et al. l74/ll RX Primary Examiner-John W. Caldwell Assistant Eraminer- -RobertJ. MooneyAttorney-Dean S. Edmonds, Harry C. Jones III et al.

[57] ABSTRACT In order to accurately and instantaneously measure theaverage temperatures of a plurality of intervals of a length of currentcarrying conductor such as a hightension cable, a plurality of pilotwires each having a conductivity which varies according to itstemperature is provided in thermal communication with correspondingintervals of the conductor along their common extents, so that theconductor and pilot wire are at essentially the same temperatures butare electrically insulated from one another. A circuit is provided formeasuring the conductivity and thereby the temperature of each pilotwire, and a radio telemetry transmitter transmits this information to areceiver on the ground, from which it may be re-transmitted to anydesired remote location.

3 Claims, 8 Drawing Figures TRANSMITTER Patented July 24, 1973 2Sheets-Sheet 1 FIG. I

III

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INVENTORS JOHN SHERMAN ENGELHARDT LAWRENCE CHARLES EBEL ATTORNEYS X-TolQSCILLATOR Patented July 24, 1973 2 Sheets-Sheet TRANSMITTER INVENTORSJOHN SHERMAN ENGELHARDT LAWRENCE CHARLES EBEL BY PM I W,

,T-yfl {AM ATTORNEYS TEMPERATURE MONITORED CABLE SYSTEM WITH TELEIVIETRYREAD-OUT CROSS REFERENCE TO RELATED APPLICATION This application is adivision of my application Ser. No. 839,571, filed July 7, 1969, nowU.S. Pat. No. 3,633,191, a continuation-in-part of application Ser. No.580,762, filed Sept. 20, 1966, now U.S. Pat. No. 3,491,597.

BACKGROUND OF THE INVENTION It is often desirable to monitor theconductor temperature of electrical transmission lines, and particularlyto have information on the temperature of relatively long lengths ofsheathed high-tension transmission cables. Underground cableinstallations, for instance, particularly in arid locations, imposesevere restraints on the thermal ratings of transmission cables. In suchlocations, the moisture content of soils is low and unpredictablyvariable so that thermal design calculations cannot be as accurate as isdesirable. In certain climates, the unpredictability of weatherconditions makes it desirable to keep a continuous watch on thetemperature of transmission lines.

It is known to measure, for instance by thermocouples, the temperatureat various points along thesheath of a transmission line, and thisprovides accurate temperature information at those discrete points.Conductor temperatures have, in the past, been derived from tables basedon laboratory measurements of cable properties, field measurements ofsoil and weather conditions over the intended right-of-way, and generalexperience. A direct knowledge of the average conductor temperature isuseful not only as an indication of operating temperature, but toprovide a more accurate understanding of the thermal properties oftransmission systems. It is not feasible, however, to provide asufficient number of thermocouples to determine the temperaturedistribution along an entire transmission line.

BRIEF DESCRIPTION OF THE INVENTION It has been discovered that anaccurate and instantaneous indication of avrage temperature along agiven length of transmission line conductor can be determined bymeasuring the temperature-dependent changes in conductance of conductivemeans in .the form of a pilot wire embedded in orotherwise maintained inthermal communication with the conductor. Such wire is embedded in theconductor when it is manufactured, and is electrically insulated frombut in thermal communication with the conductor.

It is advantageous to electrically short circuit the pilot wire to theconductor at one end of the length to be monitored, whereby the cableitself may be used as a return conductor. Since the cable conductor andthe pilot wire are atthe same temperature, any error is eliminated whichmight otherwise be present due to a temperature difference between the:pilot wire and return conductor.

Power for making the conductance measurement is preferably derived fromthe cable itself, for instance through a transformer coupling to thecurrent-carrying conductor. Since DC current is-used for themeasurement, the AC current derived from the cable may be rectified and,if desired, regulated before being fed to the measuring apparatus. Themeasuring apparatus output is connected to'control'a telemetrytransmitter for transmitting the measured value or values to a receiverat a ground station, thereby avoiding any direct electrical connectionbetween the high-tension environment where the measurement is made andground.

According to one feature of the invention, the complete apparatus formeasuring average temperature and for transmitting the measured value toa receiver is mounted on a pothead, so that instantaneous, reliablemeasurements may be directly obtained in the field. This precludes anymeasurement error from sources between the sensor (the pilot wire inthis case) and the transmitting equipment. The housing for the apparatuson the pothead is preferably electrostatically and magnetically shieldedfor accurate readings.

In one embodiment of the invention, a plurality of pilot wires isprovided either in a single conductor or in several conductors ofmulti-conductor cable which are at essentially the same temperatureswhereby the average temperatures of individual segments of theconductors may be selectively read out.

DESCRIPTION OF THE DRAWINGS The invention will be further described withreference to the accompanying drawings, in which:

FIG. 1 is an elevational view of a temperature measuring andtransmitting apparatus mounted on a pothead according to the invention;

FIG. 2 is a schematic circuit diagram of a temperature measuring andtransmitting apparatus housed in the pothead shown in FIG. 1;

FIG. ,3 is a schematic circuit diagram of the biphase bridge modulatorshown in FIG. 2;

FIG. 4 is an elevational view showing the measuring and transmittingapparatus mounted on the corona ring of an insulator according to theinvention;

FIG. 5 is a top view of the pothead housing of FIG.

FIG. 6 is a detail view of the transmitting antenna of FIG. 1;

FIG. 7 is a sectional view of a high-voltage transmission cable with amultiple conductor pilot wire embedded in its core; and

FIG. 8 is a schematic circuit diagram of an embodiment of the inventionfor determining the average temperatureof a plurality of segments of atransmission cable.

FIG. 2 shows an embodiment of the invention in which the degree ofimbalance of a Wheatstone bridge circuit istaken as an indication of theconductivity change of the pilot wire. A pilot wire 10 is embedded inthe current-carrying conductor indicated schematically as 1 1 when thelatter is manufactured. Nickel is a satisfactory material for the pilotwire. Since the method of the invention is based on the assumption thatthe pilot wire and the conductor to be monitored are at the sametemperature, the electrical insulation between pilot wire andconductormust permit thermal communication between them. If the cableinsulation is oil saturated, the pilot wire insulation should beinsolnectedrAt-the other-end ofthe length of cable, the pilot wire isbrought out of thepothead through a pressure fitting (not shown). Thepilot wire and the return conductor 11 (in this embodiment one of theconductors of the cable) are connected in series as one arm of theWheatstone bridge 12. The other three arms may comprise fixed resistorsl3, l4 and 15 as well as resistor 16 with a variable center tap forsetting the bridge at the null point. A DC voltage is applied across onediagonal, between terminals 10 and 20, and the bridge output is derivedacross the other diagonal. The DC current source, shown schematically bythe broken line 21, includes an AC power source 22 and a rectifier 23.The AC power source in FIG. 1 is a transformer, the primary winding ofwhich is the current-carrying conductor 11 of the transmission cable.The secondary winding 24 of the transformer is connected to the outputterminals of the AC power source 22, which are connected to rectifier23. The rectifier 23 in FIG. 1 may be a full wave diode bridge circuitsuch as is well known in the art.

A voltage regulator 27 may be connected to the output of the rectifier23 for providinG a constant DC output to the Wheatstone bridge terminals19 and 20. Such regulators are well known in the art.

Suitable filtering means is provided at the output of the rectifier forsmoothing the output signal. Such filtering means in FIG. 2 includes aninductance 25 and a capacitance 26. Additional filtering is provided bya large capacitor 17 connected across the seriesconnected pilot wire andreturn conductor for reducing any AC voltages inductively generated ineither of those conductors.

The DC current source 21 may alternatively be a constant voltagebattery, which may be charged by current derived from the AC current inthe cable conductor 11.

The output voltage from the Wheatstone bridge circuit is connected tothe input of a radio-telemetry transmitter 28 which, in this embodimentof the invention, is a biphase modulator in order to minimize any radiointerference from electrical discharges or transients in the powercable. Transmitter 28 includes a voltage-controlled oscillator 29, abiphase modulator 30 and a power amplifier 31, and its output isconnected to a transmitting antenna 32 which, as shown in FIG. I, ismounted integrally on the pothead housing. Power for the transmitter 28may be supplied from the output of voltage regulator 27. Voltagecontrolled oscillator 29 provides at its output a modulating signal, thefrequency of which varies in accordance with the applied input voltage.The voltage controlled oscillator preferably has an output frequency onthe order of 500Hz. and may be any type of an oscillator or othervoltage-to-frequency converter familiar to those skilled in this artwhich is compatible with the terminal and environmental conditions ofthe system.

The output of voltage controlled oscillator 29 is connected to a biphasemodulator 30, more clearly shown in FIG. 3. Modulator 30 includes acrystal-controlled oscillator 33 for providing a constant frequencycarrier signal, which is connected across one diagonal of diode quad 34through a transformer 35, permitting the diode quad 34 to operate in abalanced mode. Diode quad 34 includes diodes 36, 37, 38 and 39, as wellas R.F. chokes 40, 41 and 42 for blocking the carrier signal whilepassing the modulation signal.

Variable resistor 43 may be included in the input circuit for adjustingthe input level, as well as a filtering capacitor 44. When a positivemodulating signal is applied the input of modulator 30, it forwardbiases diodes 36 and 38, which consequently present a very low inputimpedence to the R.F. signal generated by oscillator 33, coupling thatsignal to the R.F. output terminals 45. When a negative input signal isapplied to modulator 30, diodes 37 and 39 become forward biased, passingthe RF. signal to output terminals 45 180 out of phase relative to theoutput signal produced by a positive input voltage, thereby furnishingthe desired differential phase shift function. The arrows shown in solidand dashed lines in FIG. 3 indicate the respective current paths for thepositive and negative modulating voltage input conditions.

The isolation of the non-conducting diodes is enhanced by virtue of theback bias applied to them by the modulating voltage. It will be seenthat the magnitude of the phase shift in the output signal at terminals45 is independent of the modulating voltage amplitude.

The output of the biphase modulator is connected to a power amplifiercapable of providing about 12 milliwatts output power, which has beenfound satisfactory for the purpose of this embodiment of the invention.The output of power amplifier 31 is connected to a transmitting antenna32 which, as described above, is mounted integrally with housing 46 (seeFIGS. 1 and 5).

As shown in FIG. I, the apparatus shown schematically in FIG. 2 ismounted in a housing 47 formed as an extension of a pothead whichterminates the length of conductor 11. The housing may be made ofaluminum or any electrically conductive material, for shielding and itsedges should be rounded for corona shielding. If further coronashielding is found necessary, corona rings (not shown) may be added tothe housing. Antenna 32 is a flush mounted 180 section of a rightcylinder (commonly referred to as a fiush antenna) having, for an outputfrequency on the order of MHz., an 8-inch diameter and being about 8inches in height. It is omnidirectional and vertically polarized. Asshown more clearly in FIG. 6, antenna 32 includes a flat electricallyconductive metal plate 53 to which is attached to a cylindrical wall 54made of a material transparent to the radiating frequency of theantenna. Commonly, such material is a plastic such as an acrylic. Theantenna is fed by a coaxial cable 55 coupled to an upstanding rod 56 orsimilar radiating element which extends into the cavity formed betweenplate 53 and wall 54. The exact dimension of the antenna in any givenapplication will be dependent upon the frequency to be transmitted.

Magnetic shielding from the fields generated by the conductor currentmay also be provided by means of a laminated iron casing (not shown)around the apparatus. In addition, wires within the apparatus as well asall components thereof should be positioned to minimize any inductivepickup from the circumferential magnetic field. To minimize the effectsof induced AC or surge currents, a large capacitance 34 may e connected(FIG. 2) in parallel with the output of bridge circuit 12.

Alternatively, the transmitter may be housed in a separate shieldedhousing 49, as shown in FIG. 4, preferably having a diameter compatiblewith that of the transmitter antenna 50, mounted on a corona ring 51extending about pothead 52.

Any receiver capable of receiving the output signal generated by antenna32 (or, more generally, which is compatible with the particulartransmitter and modulation mode chosen) may be used. Such receiver may,for example, have a vertically polarized whip antenna. In theabove-described embodiment of the invention, the

use of a vertical polarization mode minimizes interference fromhorizontally polarized standard FM broadcast signals. The receivingantenna is preferably located about to 50 feet from the transmittingantenna, which has been found satisfactory for good reception in thepresence of strong corona noise.

The potentiometer 16 and variable resistor 43 should be adjusted afterinstallation of the apparatus to obtain substantially zero outputvoltage from bridge circuit 12 (i.e. the bridge is nulled) at someconvenient reference temperature below the temperature range over whichthe cable is expected to operate. Any rise in conductor temperature willthen produce an increase in the resistance of the pilot wire 10, whichincrease will cause a variation in the V.C.O. input voltage byunbalancing the bridge. The degree of imbalance may be empiricallyrelatedto the rise in temperature of the pilot wire at any known valueof current in the conductor 11.

From a knowledge of the average temperature at any given time as well asthe thermal characteristics of various segments of the length of cablebeing monitored, the temperature at any given point on the cable may beaccurately estimated.

In the circuit of FIG. 2, if a length of cable approximately 3,000 feetin length is to be monitored, and the pilot wire shown is about N o. 18copper wire, the series resistance of the pilot wire and the conductor11 at 25 C. will be about 18 ohms. In this case, resistances 13 and 14may be 18 and ohms respectively, and resistance 15 may be l5 ohms.

In accordance with a particular embodiment of the invention, apparatusis provided for measuring the average temperatures of a plurality ofindividual segments of a single cable conductor, or of individualsegments of several cable conductors in a common conduit or whichotherwise have equal conductor temperatures at all cross-sections.

For monitoring a single cable conductor, a multiconductor pilot wire maybe used as shown in FIG. 7, which is incorporated into the cable in thesame manner as a single-conductor pilot wire. FIG. 7 shows afour-segment cable conductor 57 having opposite segments 57a and 570separated from segments 57b and 57d by treated paper insulation tominimize skin effect. The conductor is wrapped in a plurality ofinsulating layers indicated generally as 58 encased in an outerinsulating layer 59. Pilot wire 60 extends along the core of thesegmented conductor and includes conductors 61, 62 and 63 which areelectrically connected to segmented conductor 57 at separated pointsalong the cable, the intervals between such points being those overwhich average temperatures may be determined.

' FIG. 8 illustrates an embodiment of the invention wherein a hightension cable conductor 11' contains a pilot wire 60 extending along itsentire length, each conductor of the pilot wire 60' being connected tothe cable conductor at a respective point denominated by an x and theintervals between these points being denominated a, b, and c. The rightend of cable 1 1' terminates in a pothead (not shown) such as that ofFIG. 1 having a housing into which the three pilot wire conductorsextend. Each conductor is connected to a respective Wheatstone bridgecircuit such as Wheatstone bridge circuit 12 shown in FIG. 2, the outputof which is connected to a respective voltage controlled oscillator. Thepilot wire conductor connected to Wheatstone bridge circuit 64 extendsalong the entire length of conductor interval of a, b, and c; thatconnected to Wheatstone bridge circuit 65 extends the length of intervalb and 'c; and the pilot wire conductor connected to Wheatstone bridgecircuit 66 extends only along interval c of the cable. Bridge circuits64, 65 and 66 are connected to respective voltage-controlled oscillators67, 68 and 69, which produce modulation signals correspondingrespectively to the average temperatures of intervals a, b and c,intervals b and c and interval 0 of cable conductor 11'. The outputs ofthe voltagecontrolled oscillators are connected to a three-channeltransmitter similar to transmitter 28 so that the output of the receiverindicates an average temperature corresponding to each of the lastmentioned cable intervals. The average temperatures of each interval a,b and 0 can then be determined by simple arithmetic opera tions onvarious ones of the received signals, if the lengths of the respectiveintervals are known. For example, the average temperature of interval ais T(a) [T(abc)L(abc) T(bc)L(br)]/L(a) where T(x) is the measuredaverage temperature of the interval at and L(x) is the length of thatinterval. All of the measuring and transmitting apparatus shown in FIG.8 may, similarly to the embodiment of FIG. 2, be contained in a housingmounted on the pothead. As stated above, in severe electricalenvironments, such housing is preferably conductive. A preferred form ofsuch housing is one constructed of fiberglass or a similar moldablematerial, coated with a conductive paint. If desired, the severalWheatstone bridge circuit outputs may be connected to a single channeltransmitter by a multiplexer such as will be familiar to those skilledin this art.

For measuring the average temperatures of plural intervals of amulti-conductor cable, referred to above, one pilot wire may be providedin each such conductor and the respective pilot wires connected to theirassociated cable conductors at points corresponding to the intervals ofFIG. 8. Single channel transmitters on each pothead terminating aconductor may then transmit over different frequencies, for instance, toa common receiver.

It will be apparent that the invention is not limited to the specificfeatures in the above-described preferred embodiments, and that variousmodifications may be made without departing from its scope as defined inthe claims.

We claim:

1. Apparatus for measuring the average temperatures of a plurality ofintervals of a length of current carrying conductor, comprising;

a plurality of conductive means equal in number to the number of saidintervals to be measured, the conductivity of which vary according totheir temperature, electrically insulated from the current carryingconductor along their common lateral extent and in thermal communicationtherewith along substantially their entire lengths, so that theconductor and the conductive means are at essentially the sametemperatures, one end of each of said conductive means being connectedto the said conductor such that each conductive means spans a differentnumber of such intervals; and

transmitting signals representative of the conductance of each of saidconductive means.

3. Apparatus as defined in claim 2 wherein said length of currentcarrying conductor terminates in a pothead, including an electricallyshielded housing mounted on said pothead and containing the measuringmeans and radio transmitter; said radio transmitter including a flushantenna mounted integrally on said housing.

UNITED STATES PATENT OFFIQE CERTIFICATE CORRECTION 3,748 ,655 Dated July24, 1973 Pateot No. I

' JOHNSHERMAN ENGELHARDT ET AL Inventofls) It is certified that errorappears in the above-identified patent and that said Letters Patent arehereby corrected as shown below:

On the Certificate of Correction of November 27, 1973 the inventors nameshould be changed JOHN SHERMAN ENGLEHARDT ET AL from:

to: JOHN SHERMAN ENGELHARDT ET AL Signed and sealed this 1st day ofOctober 1974.

(SEAL) At'test;

McCOY M. GIBSON JR. C. MARSHALL DANN At testing Officer Commissioner ofPatents FORM po'wso H069) USCOMM-DC coon-pea II US. GOVIIIMINT I'IINTINGOIHCI 19., 0-36l-Jlt lJNl'll'Il) S'IA'IES PA'IEN'I ovum: CERTIFICATE OFCORRECTION Patent No. 3 748 655 Dat d July 24 1973 inventor) JOHNSHERMAN ENGLEHARDT ET AL It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

ABSTRACT I I line 10, before the period and after "another" along theircommon lateral extent" should be inserted.

Column 1, line 43, "avrage" should read -average;

line 51, before the period and after "conductor" along their commonlateral extent-- should be inserted.

Column 3, line 21, "providinG" should read providing-.

Column 4, line 4, "impedence" should read impedance;

line 26,"46" should read 47-;

line 59 "may e" should read may be Column 5, line 59, "wire 60'" shouldread wire (not shown)-;

line 60, "wire 60'" should read wire" line 62, the X should read --"x".Column 6 line 24 "T(bc)L(br) should read T(bc)L(bc) line 44, "transmit"should read -transmit--.

Signed and sealed this 27th da of November 1973.

(SEAL) Attest:

EDWARD 1 'I.PLETCHER,JR. RENE D. TEGTMEYER Attestlng Officer ActingCommissioner of Patents FORM F G-1050 (10-69) 7 US'COMM-DC 60376-P69U43. GOVERNMEN PRINTING O FICE: I959 0366-33l.

1. Apparatus for measuring the average temperatures of a plurality ofintervals of a length of current carrying conductor, comprising; aplurality of conductive means equal in number to the number of saidintervals to be measured, the conductivity of which vary according totheir temperature, electrically insulated from the current carryingconductor along their common lateral extent and in thermal communicationtherewith along substantially their entire lengths, so that theconductor and the conductive means are at essentially the sametemperatures, one end of each of said conductive means being connectedto the said conductor such that each conductive means spans a differentnumber of such intervals; and means for measuring the conductance ofeach said conductive means.
 2. Apparatus as defined in claim 1 includinga radio transmitter connected to said measuring means for transmittingsignals representative of the conductance of each of said conductivemeans.
 3. Apparatus as defined in claim 2 wherein said length of currentcarrying conductor terminates in a pothead, including an electricallyshielded housing mounted on said pothead and containing the measuringmeans and radio transmitter; said radio transmitter including a flushantenna mounted integrally on said housing.